Electrical musical instrument



VOL l/ME AND TONE C ON TROLS fl D 'HMPL IF/ E VOL UME AND TONE CON TR 0L5 0ND AMPLIFIER J. M. HANERT ELECTRICAL MUSICAL INSTRUMENT Filed May 29, 1941 Sept. 8, 1942.

CONTROLLED .YONE FREQ uavc '1' 5 Y5 TEM #4 w/va PUSH- PULL OUTPUT oPkmvo RANGE) KE r sw/rcw coureouzo TONE FREQUENCY GENERnT/Nr;

5 rs TEM HA VIA/G Push- Pl/LL OUTPl/T (AL r0 RANGE) K5 Y .sw/rc/v co/vreouao ro/vE FRE UE/var GENERATING 5 Y5 TEM H4 Wm; PUSH PULL OUTPUT (TE/v02 MAME) KEY SWITCH CONTROLLED TONE FkEQuE/vcr a ENE/2A TING 5 rs TEM ,sw w/va PUSH- P02 1. OUTPUT (B455 RAN E) Patented Sept. 8, 1942 2.295.524 ELECTRICAL MUSICAL INSTRUMENT John M. lianert. Wilmette, 111., asslgnor to Hammond Instrument Company, Chicago, 111.,

a corporation of Delaware Application May 29, 1941, Serial No. 395,755

8 Claims.

My invention relates generally to electrical musical instruments, and more particularly to improvements in the controls therefor, whereby improved musical eilects'may, be obtained.

It is one of the principal objects of my invention to provide an electrical musical instrument with improved means for obtaining octave coupier effects.

A further object is to provide an improved electrical musical instrument having a plurality of tone generating systems under the control of a single keyboard in which means common to all or a plurality of the generating systems is provided for controlling the introduction of octave coupler tones.

A further object is to provide improved key A operated switch circuits for controlling the transmission of the tone frequency signals from a generating system to the output of the instrument.

A further object is to provide an improved key operated switch for controlling the introduction of octave coupler ei'lects and improving the tone quality of the signals produced by a generating system. 1

A further object is to provide an electrical musical instrument having a plurality of generating systems. each providing tone frequencies throughout a limited pitch range. and'providing a signal transmission system for each generating system which is effective to attenuate frequencies other than those within the pitch range of its associated generating system.

Other obiects will appear from the following description, reference being had to the accompanying drawing which shows a schematic wiring diagram of the instrument.

The invention is particularly suitable for incorporation in an electrical musical instrument of the quartet organ" type-that is, an instrument having a generating system, amamplifying and transmission system, and a speaker foreach part of the multi-part harmony music. The underlying principles of instruments of this character are disclosed.in the co-pending application of Laurens Hammond, Serial No. 387,113, filed April 7, i941.

In one form that instruments of this type may assume, there is a soprano, an alto, a tenor, and a bass oscillator, each of which may oscillate at any musical tone frequency within the range of melodic parts by their respective generating, transmitting and speaker systems. Thus, in this type of instrument, the speakers may bespacial- 1y separated and the instrument may thus be used effectively for the accompaniment of multipart harmony singing, as by quartets, choirs and congregations.

The generating systems may be of any one of a number of different well known types, (such as are shown, for example, in the following Patents to Yungblut No. 2,045,172, Hammond and Hanert application Serial No. 387,113, filed April 7, 1941, and Hanert Patent No. 2,254,284), and are therefore illustrated in the drawing as blocks. Block i0 represents the generating system for the soprano range, block Ii represents the generating system for the alto range and blocks l2 and II represent the generating systems for the tenor and bass ranges respectively. Each of these blocks iii to It is intended to represent also the keyboard and key operated switches by which the frequency of the generating system output is controlled, it being assumed for present purposes that the outputs of the generating systems are of the push-pull type such, for example, as that disclosed in my patent application Serial No. 361,-

064,flled October 14, 1940.

matically cause the production of the separate The generating systems It to I! may be similar in construction except that each will be adapted and designed to produce tones within its particular range, as for example, the soprano generator may be adapted to produce the tones A2# to G4" inclusive (233.08 to 587.33 0. p. s.) the alto generating system from the note G2 to the note Di inclusive (196 to 587.33 c. p. s.); the tenor gen-, erating system from the note A1# to the note F3# inclusive (116.54 to 369.99 0. p. s.); and the bass generating system from the note C0 to the note Di inclusive (32.703 to 73.416 c. p. s.).

The push-pull output of the generating system it is supplied through conductors It and II which are connected by a radio frequency by-pass condenser CI. The conductors it and Ii are connected through blocking and current limiting condensers C2 and C3 to the control grids I. and ll of control tubes l8 and is respectively.

The tubes 18 and I! are preferably remote cutoff pentodes such as the 6K7G type. The plates 20 and 2| of these tubes are connected to a source of plate current indicated as +300 v. through load resistors R2 and R3 respectively.

The screen grids", 23 of the tubes I3 and I. are'connected to the potential source +300 v. through a voltage dividing network comprising resistors R4 and R5, the latter resistor connect ing the screen grids 22 and 20 to ground. This network is such as to maintain a voltage of +150 v. on the screen grids.

The suppressor grids 20, 21 of the tubes i and II are respectively connected to their cathodes 24, 2!, and both are connected to ground through a cathode condenser Cl. The cathodes 24, 2| are connected'through a self-bias resistor R1 to a terminal 20, the potential of which is controlled by the operation of the playing keys. The terminal 2| is connected through a resistor R8 to a source of potential +300 v., and is adapted, upon closure of any one of a plurality of playing key operated switches 20, to be connected to ground through a spark suppressing resistor R0. The terminal 20 is connected to a point of fixed D. C. potential, such as ground, through an envelope controlling condenser Cl.

It will be understood that there is a switch ll operated by each of the playing keys associated with the generating system II, the switch being preferably arranged to be operated after the playing key has operated the switch controlling the tuning of the generating system il, in a manner similar to that disclosed in my copending application Serial No. 274,325, filed May 18, 1939, which has matured into Patent No. 2,254,284, issued September 2, 1941.

It will be understood that the cathodes 24 and 2| are normally maintained at a positive voltage of +300 v. supplied through the resistor R0, thus completely cutting off the space current through the tubes it and II. Thetransmission of a signal through inter-electrode capacity is prevented due to the electro-static shielding effect of the screen grids 22 and 22 which are maintained at a fixed voltage of +150 v. by the voltage divider resistors RA and RI.

Because of the relatively high positive potential upon the cathodes 24, 2| it is preferable that a separate source be provided for the heaters 32 of each of these tubes in a well known manner, and that the heater circuit be connected to the oathodes of these tubes so as to prevent large differences in potential between the cathodes and the heaters.

The grid- I0 is connected to ground through a grid resistor Bil, whereas the grid I! may be connected selectively either to ground through a resistor RH by operation of a single-pole doublethrow switch 80 (when the latter is in the position it is shown in the drawing), or may be'connected through a conductor 20 and a resistor Rl2 to a source of constant direct current potential indicated as -150 v. When the control grid I1 is connected to ground through its resistor RI I, the tube II will operate to transmit and amplify the signal, whereas when the switch 80 is moved to a position opposite to that shown in the drawing, the control grid I! will be maintained at a -l50 v. potential, which will effectively cut of! space current flow through the tube ll.

The conductor 80 may be connected to ground by closure of a switch 40. Thus, when the switch "is closed, the position of the switch 30 will be immaterial. The purpose of the switch I will hereinafter be more fully described.

The tubes II and I0 receive signal pulses from the generating system through current limiting condensers C2 and C2. These grid signals are relatively large (in the order of 40 peak volts), and thus cause non-linear modulation of the plate current resulting in musically desirable harmonic distortion in the output signal. 0n the negative swing of the grid voltage the tubes II and I.

closely approach cutoff, and thus, positive pulses mainly are effective to cause plate current flow, as is more fully disclosed in my co-pending application Serial No. 395,754, filed May 29, 1941. The signals supplied by the generating system ll through the conductors i4 and II are preferably out-of-phase. as disclosed in said application.

The tubes II and II, being remote cutoff tubes, operate in a manner to suppress the sharp curvature of their input wave on the negative swing of this wave, that is, in a direction causing plate current cutoff. Thus, these tubes, while introducing desirable harmonic content into their output waves, do not introduce undesirable high frequencies which would be associated with peasing through the cutoff point of a sharp cutoff tube (such as the 6.170 type).

The outputs of the tubes II and Il are supplied to a common terminal 42 through condensers Cll and CH, series resistors all, an, R." and RH respectively. The Junction of the resistors RH and RI. is connected to ground through a condenser Cl2, while the corresponding junction between the resistors Rll and RI! is connected to ground through a condenser Cll. The condensers CI. to Cl! and the resistors all to R" together form a filter network effective to attenuate frequencies lower than the fundamental frequency of the lowest note of the soprano part (A240, and also to attenuate musically undesirable high frequencies (e. g. above 6000 c. p. s.)

To produce the octave coupler effect, the values of resistors RH and RI. are made approximately one half that of the corresponding resistors Rll and RH. By making these series impedance. differ from each other, exact frequency doubling is thus avoided, and the effect of the octave is produced. Every other pulse of the combined -wave is smaller in amplitude, and thus the output contains a preponderance of even numbered harmonica.

'Iheterminalflisconnectedtothecontrol grid 44 of a power output pentode ll, preferably of the one type, this connection being through a current limiting condenser C. This condenser is also made current limiting for the lowest fundamental frequency of the soprano range and is in effect an additional stage for the filtering system previously described. The value ofthecondensercltissochosenwith to the value of a grid resistor RI! that attaination of frequencies lower than the fundamental frequency of the lowest note (Mt!) of the soprano p rt is afforded. The grid resistor all is connected to a terminal of fixed negative biasns potential indicated as 28 v.

The suppressor grid ll of the tube ll is internally connected to the cathode ll of this tube. whileitsscreengridflisconnectedtoafiaed potential source indicated as +300 v. through a protective resistor R20. The plate 04 of the tube is is connected to the plate current supply source indicated as +300 v. through the primary winding I. of an output transformer it, the primary winding being shunted by a condenser Cll. The secondary winding ll of the output transformer I8 is connected in a suitable manner to a speaker 02. The condenser Cll functions as a further means for suppressing undesirable high frequencies (e. g. above 6000 c. p. s.) in the sound as heard from the soprano speaker.

, It is to be noted that attenuation of undesirable low and high frequencies is accomplished at s,sss,sss

c. p. s. (A280.

'nie volumeof theoutputiscontrolledby selcctiveoperatfon of a plurality of switches 04 to It. The switches to I. are

respectively shunted by resistance capacity meshes II to ll.

These meshes are of graded values so that by opening selected ones oithese switches, a wide dynamic range is made available. Also, base compensation is afiordcd at lower volume levels by increasing the impedance of the condenser relative to the value of the associated resistance.

This has compensation is desirable musically to produce the effect of uniform tonal response, and is necessary because of-the varying frequency response of the ear at various amplitude levels.

The generating system II, II and it for the alto. tenor and bass parts are provided with output and control systems similar to that above described for the soprano generating system it, it being understood, however, that the constants of the electrical elements differ to accord with the range of frequencies of the difierent generating systems. The various stages of the filtering system are thus made to correspond with the irequencies to be transmitted. For example, the

I filtering circuits for the alto output system may -havsthe eflect of a band-pass filter passing the frequencies from 190 c. p.s. to 5000 c. p. s. The

filtering circuits for the tenor output system similarly may be made to pass frequencies from as c. p. s. to 3000 c. p. s., and the filtering circuits for the bass output system may pass frequencies from 32 c. p. s. to 1000 c. p. s. This frequency selective arrangement of the output'circults of the various parts isalso carried out in the speaker and speaker bafile construction.

Thus. while the over-all acoustic output of the instrument extends throughout the complete range of the tones to be produced, (including their musically desirable harmonics), the individual output of each system is limited to its respective frequency range. Thus, undesirable keying transients as well as the undesirable high frequencies are suppressed in the individual generating and transmitting systems without affecting the frequency response of the other systems.

The fortuitous results of this arrangement which flow from utilising a separate transmission and output system for each pitch range of tones may be readily appreciated by considering a specific example. Let us assume that incident to the operation of the key switches of the generating system II for the soprano range, a low frequency transient of 60 cycles is generated. The filtering system of the soprano transmission system very efiectively attenuates this frequency.

transmission and output system. such attenuation of the 00 cycle frequency would render the bass generating system relatively ineffective. Conversely, highfrequency transients generated in the bass generating system It are very substantially attenuated in its transmission and output system, without in any way affecting the transmission of the desired high frequencies produced by the soprano generating system II and transmitted through its control. transmission,

and output system.

A further advantage of utilizing a separate transmission and output system for each of the generating systems'resides in the fact that harmonic distortion in the speakers or in the am plifier tubes It, or in both, does not have any detrimental musical elect. Such distortion does not produce cross-modulation between the voices, but results merely in adding harmonic overtones. Th resulting eflect is that of a slight change in tone quality, which is a distinct musical advantage, since a wide distribution of harmonic overtones is desirable when tones are sounded at high amplitude levels. By permitting harmonic distortion in the amplifier tubes and speakers, much greater acoustic output may be produced than would normally be permitted when these ountput tubes and speakers are operating strictly linearly as ("Class A") amplifiers. This results in great economy, especially in installations in which a very high amplitude level acoustic output is required.

In the operationoi the instrument, the player will normally have the switch It in the position in which the resistor RH is connected to the conductor It so that by closure of the switch 40, the octave coupler effect will be obtained in all four musical parts. whereas when the switch It is opened, the tubes ll of all four parts will be renderednon-conducting and the octave coupler eflect will be eliminated from the outputs of the four speakers. When the switch II is open, the player may, by operation of the switch ll, cause th soprano part alone to produce the octave coupler sheet, and thus be musicalLv difierentiated from the three other voices. As a result, when using the instrument to accompany singing I by large congregations, the melody or soprano It the Ieneratins systems fed into a common part may be made to stand out over and above the other three voices because of the fact that its tonality will be more prominent through having an individual octave coupler.

By the use of the single switch 40 and the auxiliary switch, the player ha available a means for producing marked contrast in the tone qaulity of the instrument as a whole,'and dynamic balance or unbalance, between the various parts, may readily be controlled as desired by the player, by operation of the switches 04 to I! of the various output systems.

As was previously pointed out, the tone generating systems ill to It may be of a wide variety of types such as vacuum tube oscillators, microphone pickups from mechanical vibrators. etc. In many of these types of generators the circuits are. such that when no key is depressed, the tone generators will continue in operation. It is thus important that when no keys are depressed no sound be audible from the speaker.

To accomplish this purpose, tubes It and I! are cut oil when no keys are depressed. A switch 30 is associated with each of the playing keys, being arranged to close whenever its key is depressed, thus changing th voltage of the terminal II from +300 v. (when the switch is open), to substantially ground potential (when one of the switches II is closed).

Condenser Cb is made large enough with respect to self-bias resistor R1 substantially to eliminate degeneration for frequencies within the particular frequency range of the part. By so doing, lowfrequency transients are effectively degenerated, and thus are not sounded by the speaker. However, to produce a desirable attack and decay envelope, additional means must be provided such that the plate current does not start instantaneously upon closure of any of the switches 30, and does not cease instantaneously upon opening such switches. To accomplish this, a second time constant mesh consisting of the relatively large condenser Cl, in conjunction with relatively small attack and anti-spark resistor R9, causes the potential at the Junction 28 to be limited in its rate of potential decrease upon closure of switch 30. Also, the resistor R8 of relatively high value, in conjunction with the condenser C1, limits the rate at which the potential at the Junction 28 rises upon opening of switch 30. Thus, the rate of decay as well as the rate of attack is controlled, but when playing legato, the potential at the junction point 20 is maintained at a fixed value. When playing legato, transients incident to suddenly changing the frequency of the generator system are greatly reduced by the filter circuit heretofore described. By making resistor R9 small and resistor R8 large, a desirable prompt attack with relatively slow decay is provided.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that the invention may be embodied in a variety of forms. I therefore desire, by the following claims, to include within the scope of my invention all such variations and modifications by which substantially the results of the invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument, the combination of a plurality of tone frequency generating systems having different tonal ranges, a separate output system for each of said generating systems, a separate signal transmitting system between each of said generating systems and its output system, each of said signal transmitting systems comprising a pair of channels connected to receive signals from their associated generating system in 180 phase relation, one of each of said pairs of channels being effective to attenuate the signal to an appreciably greater extent than the other, and means common to all of said transmission systems for rendering the attenuating channel of each of them ineffective.

2. In an electrical musical instrument, the combination of a plurality of tone frequency generating systems having different tonal ranges, a separate output system for each of said generate ing systems, a separate signal transmitting system between each of said generating system and its output system, each of said signal transmitting systems comprising a pair of channels connected to receive signals from their associated generatin system in 180 phase relation, one of each of said pairs of channels being effective to modify the amplitude of the signal to an appreciably greater extent than the other, means common to all of said transmission systems for rendering one of the channels of each of them ineffective, and means individual to one of said transmission systems to render its attenuating channel ineffective to transmit a signal,

3. In an electrical musical instrument, the combination of a plurality of tone frequency generating system having different tonal ranges and each providing a push-pull output signal, a separate output system for each of said generating systems, a separate signal transmitting natem between each of said generating system and its output system, each of said signal transmitting systems comprising a pair of channels connected to receive signals from their associated generating system in substantially phase relation, one of each of said pairs of channels being effective to attenuate the signal to an appreciably greater extent than the other, an electron discharge device in each oi said channels, and means common to all of said transmission systems for biasing beyond cutoff the electron discharge devices in their attenuating channels thereby to render them ineffective to transmit a signal.

4. In an electrical musical instrument, the

combination of a plurality of key switch controlled tone frequency generating systems having diflerent tonal ranges, a separate output system for each of said generating systems, signal transmission controlling devices respectively connecting said generating systems with their output systems. each of said devices comprising a pair of variable mu pentodes, key controlled means for conditioning said pentodes to transmit signals from said generating systems to said output systems respectively, and means common to all of said devices and operative to cut of! signal transmission through only on of the pentodes of each of said devices thereby to produce octave coupler effects in the acoustic output of all of said output systems.

, 5. In an electrical musical instrument, the combination of a plurality of key switch controlled tone frequency generating systems having different tonal ranges, a separate output system for each of said generating systems, signal transmission controlling devices respectively connecting said generating systems with their output systems, each of said devices comprising a pair of signal amplitude controlling circuits, key controlled means for rendering said circuits effective to transmit signals from said generating systems to said output systems respectively, a terminal forming part of one circuit of each pair, the direct current potentials on said terminals determining the amplitude of the signal transmitted by its connected circuit, two fixed potential points. and switch means for optionally connecting said terminals to either of said points.

6. In an electrical musical instrument, the combination of a plurality of key switch controlled tone frequency generating systems having different tonal ranges, a separate output system for each of said generating systems, signal transmission controlling devices respectively connecting said generating systems with their output systems, each of said devices comprising a pair of variable mu pentodes, key controlled means for biasing said pentodes to render them operative to transmit signals from said generating systems to said output systems respectively, means common to all of said devices and operative to change the bias on only one of the pentodes of each of said devices to a cutoff value.

7. In an electrical musical instrument, the combination of a plurality of key switch controlled tone frequency generating systems having all of said devices and operative to change the signal amplitude transmission characteristics of one path only oi each of said devices thereby selectively to produce octave coupler eilects in the acoustic output or all or said output systems.

8. In an electrical musical instrument, the combination oi a key switch controlled tone irequenc'y generator having push-pull output, an output system, a pair oi electron discharge devices each having a cathode, control grid and plate, input circuits for said devices connected to receive signals in push-pull from said generator, plate circuits for said devices, said plate circuits being coupled to said output system and being eiiective to transmit signals to the output system at different amplitudes, key switch controlled means for changing the direct current potential on corresponding bias controlling electrodes of said devices, and optionally operable means for changing the direct current potential on the other bias controlling electrode of only one 01' said devices.

some M. nsum'r. 

